An example of a typical light-emitting optoelectronic module may include a light-emitting assembly aligned with an optical assembly or series of optical assemblies. The light-emitting element may include a high-power laser diode or an array of high-power laser diodes operable to generate light of a particular wavelength or wavelengths. The optical assembly may include a refractive or diffractive lens, arrays or series of refractive and/or diffractive lenses, a microlens array or a series of microlens arrays operable to direct light of the particular wavelength or range of wavelengths. Together the light-emitting assembly and the optical assembly may be operable to generate (e.g., project) a light pattern of high-contrast features over a range of operating temperatures. During normal operation, the module's operating temperature may fluctuate, thereby causing the optical assembly and light-emitting assembly to become misaligned. Temperature fluctuations also may alter characteristics of the light-emitting assembly, such as the wavelength of light it generates. Both effects may strongly degrade optical performance during typical operation, therefore limiting the effectiveness or potential applications of such light-emitting optoelectronic modules to narrow operating temperatures.
For instance, a light-emitting optoelectronic module that includes a refractive lens with a focal length, and a vertical-cavity surface-emitting laser (VCSEL) array with an emission plane may be susceptible to such degradation in optical performance during typical operation. In this instance, the refractive lens should be aligned to the VCSEL array when the focal length is incident on the emission plane. Hence, the refractive lens and the VCSEL array can be aligned and mounted to a spacer. The spacer may be composed of a material having a positive thermal expansion coefficient. Typically, during operation, the VCSEL array generates a sufficiently high level of heat so to cause the spacer to expand. The expansion can cause the refractive lens and VCSEL array to become misaligned (i.e., the focal length of the refractive lens is no longer incident on the emission plane of the VCSEL array) at some operating temperatures. In some instances, this misalignment significantly degrades the optical performance of the light-emitting optoelectronic module at some operating temperatures.
In another instance, a light-emitting optoelectronic module includes a diffractive lens, such as a Fresnel-like diffractive lens or other diffractive optical assembly, and a VCSEL array arranged to emit a particular wavelength. The diffractive lens is specifically designed for the specific wavelength emitted by the VCSEL array. However, during operation, the VCSEL array generates sufficiently high level of heat so to shift the light emitted by the VCSEL array to longer wavelengths (e.g., 0.3 nm K−1). In some cases, such VCSEL arrays heat up to 80 K or even 100 K above the temperature for which the light-emitting optoelectronic module specifically was designed, thereby causing significant shifts to longer wavelengths and a concurrent degradation in optical performance of the light-emitting optoelectronic module.
In some instances, a light-emitting optoelectronic module includes a microlens array and a VCSEL array. The optical performance of such light-emitting optoelectronic modules is strongly dependent on the alignment of the microlens array and the VCSEL array, as well as the wavelength of light emitted by the VCSEL array. However, as described above, significant fluctuations in operating temperature can cause the microlens array and the VCSEL array to become misaligned due to fluctuations in material dimensions, and further can cause a shift in wavelengths emitted by the VCSEL array.